This invention relates to a flip-chip type semiconductor device sealing material and a flip-chip type semiconductor device encapsulated therewith.
With the advance of electric equipment toward smaller size, lighter weight and higher performance, the semiconductor mounting technology has changed from the pin mating type to the surface mounting which now becomes the mainstream. One bare chip mounting technology is flip-chip (FC) mounting. The flip-chip mounting is a technique of providing an LSI chip on its circuit pattern-bearing surface with several to several thousands of electrodes, known as bumps, of about 10 to 100 microns high and joining the chip to electrodes on a substrate with a conductive paste or solder. Then the sealing material used for the protection of FC devices must penetrate into gaps of several tens of microns defined by bumps between the substrate and the LSI chip. Conventional liquid epoxy resin compositions used as the underfill material for flip-chip devices are generally composed of a liquid epoxy resin, a curing agent and an inorganic filler. Of these, the most predominant is a composition in which a large amount of inorganic filler is blended in order to provide a matching coefficient of linear expansion with those of semiconductor chips, substrates and bumps for increased reliability.
With respect to stress properties, the flip-chip underfill materials with high loading of filler give rise to no problem. However, they suffer from very low productivity since they have a high viscosity and high thixotropy due to the high filler loading so that they may penetrate into the gap between chip and substrate at a very slow rate. There is a desire to overcome this problem.
It is a common practice in the art to treat the fillers with surface modifiers such as silane coupling agents for improving the affinity of the filler surface to epoxy resins and hence, the bond strength therebetween. Although no problems arise with limited amounts of fillers, materials loaded with large amounts of fillers cannot be fully improved in performance simply by surface treating the fillers with modifiers or adding surface modifiers.
An object of the invention is to provide a flip-chip type semiconductor device sealing material which maintains a low enough viscosity to ensure interstitial infiltration even when filled with a large amount of inorganic filler and which cures to form a reliable seal. Another object is to provide a flip-chip type semiconductor device encapsulated with the sealing material and having improved reliability.
The invention is based on the following discovery. In an epoxy resin composition comprising (A) 100 parts by weight of a liquid epoxy resin and (B) 0 to 80 parts by weight of a curing agent, there is blended a copolymer obtained through addition reaction between an alkenyl group-containing epoxy resin and an organopolysiloxane represented by the average compositional formula (1) to be defined below, the addition reaction taking place between alkenyl groups in the epoxy resin and hydrogen atoms attached to silicon atoms (i.e., SiH groups) in the organopolysiloxane, the organopolysiloxane units in the copolymer being 1 to 15 parts by weight per 100 parts by weight of components (A) and (B) combined. Further blended in the composition is a mixture of coarse and fine inorganic fillers having a specific surface area of less than 4 m2/g and at least 4 m2/g, respectively, as measured by the BET method. The fine inorganic filler having a specific surface area of at least 4 m2/g has been surface treated with an aminosilane or organosilazane compound represented by the general formula (2) or (3) to be defined below. The amount of the inorganic filler mixture is 100 to 400 parts by weight per 100 parts by weight of components (A), (B) and (C) combined, and preferably the fine inorganic filler having a specific surface area of at least 4 m2/g accounts for 5 to 30% by weight of the inorganic filler mixture. The resulting epoxy resin composition maintains a low enough viscosity to ensure interstitial infiltration even when filled with a large amount of inorganic fillers and is thus suitable as a sealing material for flip-chip type semiconductor devices. Flip-chip type semiconductor devices encapsulated with the sealing material remain highly reliable.
Accordingly, the invention provides a sealing material for flip-chip type semiconductor devices comprising
(A) 100 parts by weight of a liquid epoxy resin,
(B) 0 to 80 parts by weight of a curing agent,
(C) a copolymer obtained through addition reaction between an epoxy resin having alkenyl groups and an organopolysiloxane represented by the following average compositional formula (1):
HaRbSiO(4xe2x88x92axe2x88x92b)/2xe2x80x83xe2x80x83(1)
wherein R is a substituted or unsubstituted monovalent hydrocarbon group, a is a positive number of 0.005 to 0.2, b is a positive number of 1.8 to 2.2, and the sum of a and b is from 1.805 to 2.3, the addition reaction taking place between alkenyl groups in the epoxy resin and hydrogen atoms attached to silicon atoms in the organopolysiloxane, the organopolysiloxane units in the copolymer being 1 to 15 parts by weight per 100 parts by weight of components (A) and (B) combined,
(D) 50 to 350 parts by weight of an inorganic filler having a specific surface area of less than 4 m2/g, and (
E) 5 to 120 parts by weight of a fine inorganic filler having a specific surface area of at least 4 m2/g and surface treated with an aminosilane or organosilazane compound represented by the following general formula (2) or (3):
(R1)3SiN(R2)2xe2x80x83xe2x80x83(2) 
wherein R1 is independently selected from an alkyl group of 1 to 4 carbon atoms, vinyl group and phenyl group, R2 is hydrogen or as defined for R1, and m is an integer of 0 to 4,
the total amount of inorganic fillers (D) and (E) being 100 to 400 parts by weight per 100 parts by weight of components (A), (B) and (C) combined.
Also contemplated herein is a flip-chip type semiconductor device sealed with the sealing material in a cured state.